Aneurysmal expansion of the LV wall after myocardial infarction begins days after the infarct and continues for some weeks. The area appears thin and akinetic or dyskinetic (paradoxically moving outward) on echocardiography. The true aneurysm is usually shallow with a broad rim and thin wall comprised of all layers of the left ventricle: endocardium, dense fibrous scar tissue with few surviving myocytes, and epicardium. The main complications of true aneurysm are cardiac arrhythmia and intracardiac thrombus formation. A mature dilated scar rarely ruptures.

A pseudoaneurysm or false aneurysm of the LV wall occurs within a very few days after infarct. The area appears very thin, ballooning, akinetic/dyskinetic, and perhaps filled with turbulence on echocardiography. The pseudoaneurysm is usually saccular with a narrow rim and very thin wall comprised of mostly epicardium and perhaps organizing thrombus. The pseudoaneurysm reflects where the necrotic LV wall has actually ruptured and blood is extravasating into, and distending, the potential space of the visceral pericardium. The main complications of pseudoaneurysm are cardiac rupture/tamponade and thrombus formation.